DENVER - Barack Obama says Joe Biden is ready to step in as US president. He's not bad in the role of attack dog, either, wasting no time gnawing at GOP rival John McCain.

"He will have to figure out which of the seven kitchen tables to sit at" when considering his own economic future, Biden said, a blistering reference to McCain's embarrassing admission, particularly during a period of financial turmoil, that he didn't know how many homes he and his ultra-wealthy wife own.

US Democratic presidential candidate Senator Barack Obama (R) listens as his vice presidential running mate Senator Joe Biden speaks at a campaign event at the Old State Capitol in Springfield, Illinois August 23, 2008. [Agencies]

Named Obama's running mate before dawn Saturday, a feisty Biden appeared with the top of the ticket at an afternoon rally in Springfield, Ill.

He gave a speech filled with subtle jabs and outright punches at McCain, a sharp tone intended to send a message to nervous Democrats: Never fear, the vice presidential attack dog is here, and he's itching for a fight.

As polls show the race tightening, Democrats increasingly have been questioning whether Obama can play the game of brass-knuckle politics against McCain. Some are fearing a repeat of 2004 when a Republican-aligned group called the Swift Boat Veterans for Truth got the best of slow-to-respond John Kerry and his soft-touch No. 2 John Edwards.

Biden, however, left no doubt he's comfortable going for the jugular.

In one breath, he called McCain "generally a friend of mine" over a 35-year period. In the next, the Democrat skewered his decades-old Republican colleague and linked McCain to the unpopular President Bush at every turn.

"The American dream under eight years of Bush and McCain, that American dream is slipping away," Biden said, suggesting that McCain, too, served in the White House during that period and overlooking the times when the Arizona senator broke from his own party's standard-bearer.

He jabbed at McCain, a Vietnam prisoner of war who is arguably the county's most vocal supporter of the US mission in Iraq, next to Bush. Said Biden: "These times require more than a good soldier. They require a wise leader. A leader who can deliver."

The Delaware senator also used McCain's own words against him to argue that the Republican can't change the country when he offers more of the same, though he left out details and cherry-picked quotes as he sought to make his case.

He noted that McCain voted with Bush some 90 percent of the time and read McCain quotes that he said has been "totally in agreement and support of President Bush" on "the most important issues of our day," and that "in the Bush administration we make great progress economically."